Identification of C10 nitrogen-containing aporphines with dopamine D1 versus D5 receptor selectivity.

New aporphines containing C10 nitrogen substituents (viz. nitro, aniline or amide moieties), were synthesized and evaluated for affinity at human serotonin 5-HT1A and 5-HT2A receptors and at human dopamine D1, D2 and D5 receptors. Two series of analogs were investigated: series A which contain a sole C10 nitrogen substituent on the tetracyclic aporphine core and series B which are 1,2,10-trisubstituted aporphines. Remarkably, compounds from both series lacked affinity for the D5 receptor, thus attaining D1 versus D5 selectivity. Compound 20c was the most potent D1 ligand identified. Docking studies at D1 and D5 receptors indicate that the binding mode of 20c at the D1 receptor allows for stronger hydrophobic contacts, (primarily with Phe residues) as compared to the D5 receptor, accounting for its D1 versus D5 selectivity. Considering the lack of affinity for the D5 receptor (and low affinity at other receptors tested), compound 20c represents an interesting starting point for further structural diversification of aporphines as sub-type selective D1 receptor tools.